Frank shot Matt in the head and I was sold 🤣

There are honestly almost too many reasons to list. I started shipping them because of the Netflix show (and started reading comics because of that show), and I mean. That first meeting where they're so evenly matched. The next night when Matt is trying to fight Frank again wearing a mask that's clearly taped together from Frank shooting him the night before. Frank kidnapping him and chaining him up on a rooftop instead of leaving him for the cops, and even then they can't go five minutes without screaming at each other about their clashing moralities lmao. Matt carried Frank out of the line of fire twice (once after Frank killed someone in front of him), and Matt was the one Frank opened up to about losing his family. Frank clearly clocked Matt in the courtroom but never told anyone, and he showed up to save him from the Hand at the end.

In Born Again, they have this level of familiarity with each other that feels more like the comics (or like fanfiction, really!) where Matt knows where Frank's safehouse is and visits him there, but the possibility of Matt turning him into the cops never comes up. Matt can never stop trying to save Frank, and Frank can never stop trying to get Matt to join him. They're so similar, two sides of a coin, that you can see them both thinking "if I can just get this one guy to see things my way, the world might make a little more sense". But they're both too stubborn and set in their ways to move, so they just beat the shit out of each other instead lol. Frank was the one Matt opened up to about losing Foggy--and Frank had to push, but he knew Matt needed it. Their bickering in Matt's apartment, and the "yeah, I did it for you" about Frank shaving and cutting his hair which walks the line of it's a joke and it's not. Karen might have called Frank, but he still showed up.

There's also a scene in 616 comics where Matt shows up at Frank's super secret safehouse that no one can know about--except Daredevil, that's fine. Frank turns himself in and gets sent to prison so he can break Matt out. Frank rescues Matt when he's surrounded by cops. Matt can track Frank by his heartbeat. Matt calls Frank his "nemesis", his "opposite number" (Marvel Knights 2000) when I would honestly expect him to reserve "nemesis" for Bullseye or Fisk. They have the most Divorced™ energy where they cannot be in the same room for five minutes without arguing, but Frank will still save Matt and Matt will still put a collapsing Punisher into a taxi and send him home even as Frank insists he doesn't need help, and they still fight together like a well-oiled machine. The Vegas arc. The Omega Effect arc feat. Peter "right in front of my salad?" with those two. Seventh Circle where they're fighting each other the whole time but will still team up in response to a larger threat and have what is, for them, an almost civil conversation at the end. Even Garth fucking Ennis, who famously hates superheroes, will include Daredevil and the fratt situationship in his Punisher comics.

I also think [St. Vincent voice] "you're the only motherfucker in this city who can stand/handle me" really sums them up. Matt disaster Murdock gets all of his girlfriends killed, mindfucked, or breaking up with him and his bullshit if they're lucky. Frank is an indestructible cockroach fuck who would smack Matt upside the head and tell him to knock it the hell off. No time for his candy-ass shit.

As for Frank, Matt is someone he doesn't have to worry about. I can't see the Punisher "dating", but if he were to be involved with someone even semi-regularly (like Elektra in the 2013 Thunderbolts run), it would have to be someone he's not putting in danger via proximity. Matt (either as Matt Murdock or Daredevil) gets in enough trouble on his own that Frank being around isn't necessarily going to make things worse, and may provide an extra line of defense in case someone goes after him.

In short (lol), I'm going to quote myself from my fic "double vision", which is also a sort of ship manifesto at parts:

All his relationships had either been short-lived or crashed and burned as spectacularly as a pyrotechnic display, ending in death or disaster or someone storming out, sick of his lies and broken promises. He tried to imagine lying to Frank Castle and couldn’t, any more than he could imagine the man sitting at home and wringing his hands helplessly while Matt was out risking his life. Castle when he was after something was about as single-minded and determined as they came, and he’d pin Matt down and drag the truth out of him if he had to, or he’d track him down himself if he thought he had reason to worry. And, just like that, everything other-Matt said started to make an unavoidable kind of sense. He remembered Castle’s hands on him, not other-Castle, but the Frank he knew. Colliding with him when they fought, sewing his wounds shut and covering them with bandages when they worked together, the way fighting side by side with him felt like flying. Oh, Matt thought. Fuck.

And:

Frank thought again of their doubles, of how they weren’t their doubles, and nothing that happened there had to happen here. He didn’t know what the future held. But he did know the jitter of nerves he felt when he worked a job likely to bring him in contact with Red, the apprehension he always had waiting for him to show up that now looked more like anticipation. He knew now that if anyone went after Red or hurt him in a serious way, Frank was probably going to tear out their kneecaps before killing them, and his half-baked plans to go after Fisk weren’t entirely about not-owing Nelson. He liked how Red looked in his trenchcoat—he wasn’t a small man by any stretch, but Frank was a little wider in the shoulders, and it made the sleeves brush down almost to his fingertips. He liked working with Red when they could agree, and he liked making him laugh.